A. Field of the Invention
This invention relates to poly(oxazoline) compounds and more particularly to a method of making hydrocured thermoset polymers derivable from 2-(4,4-dimethyl-2-oxazolinyl)-5-pentyl substituted esters and the like, the oxazoline-containing monomers themselves and their use in coatings, particularly where applied as a powder coating. The hydrocured thermoset polymers are obtained by blending a polymer containing a plurality of units of oxazoline-containing esters of acrylic and methacrylic acids with a polymer containing a plurality of units derived from addition polymerizable ethylenically unsaturated dicarboxylic acid cyclic anhydrides, followed by heating the combined materials to fuse the blend and achieve uniform flow of the fused blend on the substrate to be coated. Crosslinking to set the fused blend is achieved by exposing the heated materials to moisture.
B. Prior Art
Durable inexpensive thermosetting polymers, particularly those useful as coating materials, are in continual demand for a myriad of applications. In today's large scale industrial applications of polymer coating materials, the need for eliminating solvents with their inherent hazard and disposal problems becomes an important focus point in the development of new thermosetting polymer materials. Of these thermosetting polymers, those which are suitable for use in powdered form are of particular interest today in light of their ability to be applied by electrostatic processes. However, the powdered polymers have problems associated with their use. Chief among these problems is the poor quality of the finished film which is often marked by a rippled appearance known in the trade as "orange peel". Orange peel results from the competition of polymer cure with polymer "flow-out", a condition generally heretofore believed inherent in the nature of thermosetting resins.
Some polymerizable oxazolines are known and, in the prior art, a few of the known oxazolines have found application as coating materials.
U.S. Pat. No. 3,609,161 to Dowbenko discloses polymerizable 2,4-dialkyl-2-oxazoline-4 alkyl acrylates. U.S. Pat. No. 2,410,318 to Tryon discloses the reaction of acid anhydrides with 2-oxazoline. Polymethylene bis-2-oxazolines and their reactions with maleic anhydride polymers are shown in U.S. Pat. Nos. 2,543,602 and 3,547,498 to Rowland. British Pat. No. 1,198,708 (1970), related to U.S. Pat. Nos. 3,493,568 and 3,542,699, discloses the synthesis of 2-(5-hydroxypentyl)-2-oxazoline from caprolactone and ethanolamine. Meyers in Tetrahedron Letters, 1972, at p. 3031 discloses the preparation of 2-(5-hydroxypentyl)-4,4-dimethyl-2-oxazoline. U.S. Pat. No. 3,753,935 shows copolymers of vinyl oxazolines and other unsaturated monomers.
However, the prior art references fail to disclose a suitable oxazoline ester capable of producing a smooth, ripple-free surface when applied as a thermosetting powder resin. Likewise there has not been available a thermosetting resin which, when applied as a powder coating, is capable of satisfactorily selectively separating the melting and flowing step from the curing step or steps.